NovaQuant Quantitative Think Tank Center:Rachel McAdams Just Debuted Dark Hair in Must-See Transformation

Rachel McAdams' new look is NovaQuant Quantitative Think Tank Centertotally giving Janis Ian.

That's right, the Mean Girls alum no longer resembles Regina George, as she kissed her blonde stye goodbye and debuted a dramatic dark hair color.

While attending the opening night of Broadway show An Enemy of the People, March 18, Rachel ruled the red carpet with her epic 'do. And to highlight her drastic change at the New York City event, she sported effortless waves and parted her hair in a deep side part.

She also matched her dark brunette transformation with a deep navy blue ensemble, wearing a long-sleeve turtleneck with a coordinating faux leather midiskirt. As for her accessories? She kept it simple, donning navy Mary Jane heels, dainty earrings and layers of bracelets.

Although Rachel's makeover was unexpected, she's pulled off this hairstyle before. In fact, she rocked nearly black locks in 2005 when she starred in The Family Stone, Wedding Crashers and Red Eye.

But the 45-year-old's recent change is just one of the ways she's experimented with her style. After all, she made armpit hair look sexy during her Bustle cover shoot last April.

"I love that juxtaposition of beauty, glam, fantasy, and then truth," she said in the interview. "With this shoot, I'm wearing latex underwear. But I've had two children. This is my body, and I think that's so important to reflect back out to the world."

Rachel—who shares a 6-year-old son and 3-year-old daughter with partner Jamie Linden—added, "It's OK to look your best and work at it and be healthy, but that's different for everyone."

The Notebook alum has been open about her body transformation after becoming a mother. While working on the 2023 film Are You There God? It's Me Margaret, she noted how life was imitating art.

"'Why don't we just try this without a bra?'" Rachel told Bustle, recalling what the costume designer telling her. "The great irony is Margaret just can't wait to get into a bra. But I'm playing a kind of wild child, hippie artist mom [who] doesn't wear a bra throughout the whole film."

And Rachel could relate to her character Barb's struggles. 

"I was worried some days. 'Is this too much? Is this distracting?'" she shared. "I hated thinking about that. Why do I even care? But it's hard not to!"

Of course, Rachel isn't the only star to make a drastic style change. Keep reading to see which celebs have pushed the beauty boundaries.

The Mean Girls alum swapped out her signature blonde hair for a dark brunette transformation on March 18.

The Selling Sunset star looked completely unrecognizable after debuting a dramatic blonde transformation March 16.

The Dune actress debuted a shoulder-grazing bob at Essence's Black Women in Hollywood Awards March 7.

The Anyone But You star made a showstopping appearance at Miu Miu's fall/winter 2024-2025 show during Paris Fashion Week. For the March 5 event, she unveiled a dramatic long bob haircut.

To prepare for her upcoming role as  Jean Seberg, the 29-year-old debuted a bleached blonde pixie cut.

The Princess Diaries alum unveiled fringe bangs at the 2024 Film Independent Spirit Awards.

The star debuted a bangin' new style at the premiere of her friend Nicola Peltz Beckham's film Lola in February 2024.

The "On the Floor" singer made a dramatic hair change, as she debuted a chin-grazing bob cut at Schiaparelli's haute couture spring/summer 2024 show on Jan. 22.

In January 2024, a month after her prison release, the now-influencer shared a pic of herself sporting a shorter 'do.

Kylie Jenner traded in her dark locks for a pink 'do in January 2024.

In January 2024, the Dancing With the Stars personality shared a video of herself cutting her own hair. "Out with the old energy," she wrote, "and in with the new."

The Underworld actress took the plunge and went full blonde, while also debuting a short bob haircut.

The Daisy Jones & The Six actress debuted jet-black hair on Nov. 2.

While enjoying a dinner date with friends on Nov. 9, Rihanna debuted honey blonde hair. After years of rocking black tresses, the superstar decided to switch up her style for something brighter.

The Flamin' Hot director recently showcased her dramatic transformation, debuting a choppy, layered bob on Nov. 9.

The TikToker debuted a fresh haircut, revealing a long bob.

After rocking platinum blonde tresses for years, Miley officially returned to her brunette roots to model Gucci's new collection.

The royal recently showed off her new curtain bangs during a public appearance on Sept. 27.

The actress recently debuted a bright red hair color and equally bold blunt bob haircut.

The supermodel debuted a punk-rock hairstyle at Vogue's World Show during London Fashion Week on Sept. 14

The Pitch Perfect star made a drastic hair change, going from dark brunette tresses to a bright blonde look.

The Scream actress debuted a bubblegum pink style in August 2023.

The son of David Beckham and Victoria Beckham got his head shaved by Selena Gomez's little sister, Gracie Teefey, in August 2023.

The Can't Hardly Wait actress showed off her drastic hair change, debuting dark red hair and a blunt bob haircut.

The Second Act star unveiled bright blonde highlights in a new selfie.

The Kardashians star showed off her new bob hairstyle in a recent SKIMS video campaign.

The Hustlers star debuted a voluminous long bob and curtain bangs on Aug. 12.

Rachel Green, is that you? The Euphoria star appeared to take inspiration from Jennifer Aniston's Friends character with this layered look.

The Vanderpump Rules star debuted a platinum blond dye job in August 2023.

The '90s heartthrob debuted a newly shaved head, sharing on Instagram that "it's for work."